Encrypted voice and data communication systems are known to comprise a plurality of communication units, a limited number of transceivers that transceive audio and data information amongst the plurality of communication units via a limited number of communication resources, and a communication resource allocator. (A communication resource may be a carrier frequency, frequency pairs, a TDM slot, etc.) Encrypted voice and data communication systems, or secure communication systems, provide secure communication between two or more communication units by sharing a particular piece of information between them. The particular piece of information is generally known as an encryption key variable, or key, which allows only those communication units possessing it to properly transmit and receive encrypted messages.
To enhance the security of the secure communication systems, the keys are periodically changed. For example, the key may be changed weekly or monthly, depending on the desired security of the secure communication system. To further enhance security of communications within the secure communication system, multiple keys may used by the plurality of communication units. By having each of the plurality of communication units able to use one of the plurality of keys, the ability for an unauthorized user to decipher a secure communication is greatly reduced.
When a communication unit receives an encryption message that it does not have the proper key for, the user of the communication unit would be presented with a garbled signal. To prevent the garbled signal from being presented to the user, the communication unit comprises a proper code detection circuit. The proper code detection circuit is used to squelch, or mute, the receiver when ever a message is received that is encrypted with a different key than the communication unit is utilizing. The proper code detection circuit, when it determines that the received message is encrypted with the same key as the communication unit is utilizing, unmutes the receiver and allows the message to be heard by the user.
As is known in communication systems, communication units are grouped together, wherein the grouping is based on commonality of use. For example, communication units operated by a police department may form one group, while communication units operated by a fire department may form another group. These groups may be further divided into sub-groups; for example, the police group may be further divided into districts. For each group or sub-group, an individual key may be needed to maintain the desired security. Even though each group or sub-group may comprise its own unique key and may share the same communication resource, a situation may arise where an operator of a console may need to communicate with all the groups and sub-groups that are sharing the same communication resource. In such instances, the operator of the console must know what key each group or sub-group was using. In large communication systems, this places a substantial burden on the operator which may distract him or her from more important tasks.
Therefore, a need exists for an automatic way to monitor and utilize multiple keys in a secure communication system.